Steam cooker

ABSTRACT

In a steam cooker, a tray-shaped case ( 51 ) of a steam temperature-raising device ( 50 ) has a recessed part ( 51   a ) into which steam from a steam generator flows through steam supply ports ( 95 A,  95 B,  95 C) provided in a first sidewall ( 91 ). The recessed part ( 51   a ) has a planar shape roughly symmetrical with respect to a center line (L) of a steam flow entering through the steam supply ports ( 95 A,  95 B, and  95 C). First and second steam superheaters ( 52, 53 ) are placed in the recessed part ( 51   a ) of the tray-shaped case ( 51 ) so as to be symmetrical with respect to the center line (L). A spiral heat radiation fin ( 56 ) having a fin pitch of 10 mm or less is wound around the first steam superheater ( 52 ). The tray-shaped case ( 51 ) is placed on a ceiling panel of a heating chamber and at steam outlets with an opening of the recessed part ( 51   a ) directed downward.

TECHNICAL FIELD

This invention relates to a steam cooker.

BACKGROUND ART

Heretofore, as a steam cooker for cooking an object to be cooked such asfood by using steam, there is a one that feeds superheated steam into anoven (for example, see JP 8-49854 A). This steam cooker has a steamgenerator in which a heater is provided in a pot to generate steam, anda steam superheater that generates superheated steam by heating thesteam generated by the steam generator, and the superheated steamgenerated by the steam superheater is sent into the oven to cook food.

Incidentally, in the conventional steam cooker, superheated steamgenerated by the steam superheater blows into the oven through a steamoutlet provided in an upper portion of a side surface of the oven, thesuperheated steam is sucked through a suction opening provided in alower portion of the side surface, so that the superheated steam iscirculated in the oven and in a circulation air passage. Therefore, inthe conventional steam cooker, airflow in the oven is biased, andtemperature distribution does not become uniform, so that uneven cookingoccurs in an object to be cooked, and cooking with a good finish cannotbe done

SUMMARY OF THE INVENTION

An object of this invention is, therefore, to provide a steam cookerthat can make temperature distribution in a heating chamber uniform andensure even cooking.

In order to accomplish the above object, a steam cooker according to thepresent invention comprises:

a steam generator for generating steam;

a steam temperature-raising device for raising a temperature of steamcoming from the steam generator;

a heating chamber provided with a ceiling steam outlet on its ceilingside, in which an object to be cooked is heated by steam supplied fromthe steam temperature-raising device via the ceiling steam outlet,

the steam temperature-raising device including:

-   -   a tray-shaped case having a recessed part which has a sidewall        provided with a steam supply port through which steam from the        steam generator enters the recessed part, the recessed part        having a planar shape that is roughly symmetrical with respect        to a center line of a steam flow entering through the steam        supply port, the tray-shaped case being placed, with an opening        of the recessed part directed downward, on the heating chamber        at the ceiling steam outlet;    -   a heater placed in the recessed part such that a planar shape of        the heater is roughly symmetrical with respect to said center        line; and    -   a spiral heat radiation fin wound around the heater and having a        fin pitch of 10 mm or less.

In the steam cooker with the above construction, steam generated by thesteam generator is raised in temperature by the steamtemperature-raising device to become superheated steam, and thesuperheated steam is supplied into the heating chamber, whereby theobject to be cooked in the heating chamber is heated. At this time,steam generated in the steam generator enters the recessed part of thetray-shaped case of the steam temperature-raising device through thesteam supply port provided in the sidewall of the recessed part which isplaced above the ceiling steam outlet of the heating chamber. Steamflowing into the recessed part, which has a planar shape (i.e., a shapein a plan view) roughly symmetrical with respect to the center line ofthe steam flow entering through the steam supply port, is divided intothe left and right side branches after colliding with a sidewall on theopposite side of the steam supply port of the recessed part, and a partof the branched steam returns along the sidewalls of the recessed parttoward the steam supply port and merges into steam entering through thesteam supply port. In this manner, steam filling the recessed part ofthe tray-shaped case is supplied into the heating chamber via theceiling steam outlet of the heating chamber located on the opening sideof the recessed part.

The planar shape, i.e., the shape in a plan view, of the recessed partof the tray-shaped case and the planar shape of the heater placed in therecessed part are individually made roughly symmetrical with respect tothe center line of the steam flow entering by the steam supply port,whereby the steam flow in the recessed part is not biased to the left orright, so that the temperature distribution in the entire recessed partof the tray-shaped case is made uniform.

Further, the fin pitch of the spiral heat radiation fin wound around theheater, which heater is provided in the recessed part of the tray-shapedcase and arranged in a planar shape roughly symmetrical with respect tothe center line, is set to 10 mm or less, whereby influence (disturbanceor resistance loss) of the heat radiation fin on the steam flow jettedfrom the steam supply port can be distributed in a manner so as to beroughly symmetrical with respect to the center line, and the steamtemperature distribution in the recessed part is made uniform, whileimproving the efficiency of heat radiation from the heater by the heatradiation fin. Therefore, by making the temperature distribution ofsteam supplied into the heating chamber through the ceiling steam outletof the heating chamber uniform, the temperature distribution in theheating chamber can be made uniform, and uniform cooking can berealized.

In one embodiment, a plurality of steam outlets for supplying steam intothe heating chamber sideways are provided, in roughly symmetricalarrangement with respect to said center line, in sidewalls facing eachother across the center line of the recessed part of the tray-shapedcase and on the opposite side of the steam supply port.

In the steam cooker of the above embodiment, the plurality of steamoutlets are provided in the sidewalls facing each other across thecenter line of the recessed part of the tray-shaped case and on theopposite side of the steam supply port, and a part of steam in therecessed part is supplied sideways into the heating chamber via theplurality of the steam outlets. By roughly symmetrically providing theplurality of steam blowout openings in the sidewalls facing each otheracross the center line of the recessed part of the tray-shaped case andon the opposite side of the steam supply port, the temperaturedistribution of steam that blows outward toward both sides of the centerline via the plurality of steam outlets can be made uniform. Thus, thebias to the left or right in the temperature distribution of steamsupplied into the heating chamber sideways can be reduced, so that thetemperature distribution in the heating chamber can be made uniform.Furthermore, by providing the plurality of steam outlets in thesidewalls facing each other across the center line of the recessed partof the tray-shaped case and on the opposite side of the steam supplyports, steam of the highest flow rate and temperature (due to heating bythe heater) in the recessed part blows out from the plurality of steamoutlets. This vigorously supplies high-temperature steam into theheating chamber. Thereby, steam in the heating chamber is agitated,which is preferred in resolving uneven cooking.

In one embodiment, a sidewall on the opposite side of the steam supplyport of the recessed part of the tray-shaped case is inclined withrespect to a plane roughly perpendicular to said center line.

In the steam cooker of the above embodiment, since the sidewalls on theopposite side of the steam supply port in the recessed part of thetray-shaped case are inclined with respect to the plane that is roughlyperpendicular to the center line, when steam flowing into the recessedpart collides with the sidewall on the opposite side of the steam supplyport in the recessed part and is divided, steam branch flows are madesmooth and generation of steam accumulation and so on causing uneventemperature distribution is suppressed. As a result, the temperaturedistribution of steam that flows in the recessed part can be madeuniform.

In one embodiment, the planar shape of the recessed part of thetray-shaped case is a generally pentagonal shape having three sidesforming a U-shape and two sides continuous with both ends of the U-shapeof the three sides and forming a generally V-shape bent outward, and thesteam supply port is provided in a sidewall corresponding to a centralone of the three sides forming the U-shape of the recessed part of thetray-shaped case.

In the steam cooker of the above embodiment, in the recessed part havinga roughly pentagonal planar shape, the two sides forming the V-shapeprojecting outward, which are continuous with both the ends of theU-shape formed by the three sides, serve as the sidewall that areinclined with respect to the plane roughly perpendicular to the centerline. Thereby, when steam flows into the recessed part through the steamsupply port provided in the sidewall corresponding to a central one ofthe three sides forming the U-shape of the recessed part of thetray-shaped case, and collides with the two sidewalls forming theV-shape on the opposite side of the steam supply port, and is bifurcatedto the left and right, the steam branch flows are made smooth, andgeneration of steam accumulation and so on causing uneven temperaturedistribution is suppressed, so that the temperature distribution ofsteam flowing in the recessed part can be made uniform.

In one embodiment, the planar shape of the recessed part of thetray-shaped case is a shape having three sides forming a U-shape and anarc-shaped outer periphery that is continuous with both ends of theU-shape of the three sides and curves outward, and the steam supply portis provided in a sidewall corresponding to a central one of the threesides forming the U-shape of the recessed part of the tray-shaped case.

In the steam cooker of the above embodiment, in the recessed part of thetray-shaped case, the arc-shaped outer periphery continuous with boththe ends of the U-shape formed by the three sides and curving outward,serves as the sidewall that is inclined with respect to the planeroughly perpendicular to the center line. Thereby, when steam flows intothe recessed part through the steam supply port provided in the sidewallcorresponding to a central one of the three sides forming the U-shape ofthe recessed part of the tray-shaped case, and collides with thesidewall forming the arc-shaped outer periphery on the opposite side ofthe steam supply port, and is bifurcated to the left and right, thesteam branch flows are made smooth, and generation of steam accumulationand so on causing uneven temperature distribution is suppressed, so thatthe temperature distribution of steam flowing in the recessed part canbe made uniform.

In one embodiment, each of corners of the recessed part of thetray-shaped case has a curved surface so that adjacent sidewalls aresmoothly continuous with each other.

In the steam cooker of the above embodiment, the curved surface isprovided at each corner of the recessed part of the tray-shaped case sothat the adjacent sidewalls are smoothly continuous, whereby the part ofsteam flowing into the recessed part flows along the sidewalls of therecessed part smoothly. Therefore, the steam flow in the recessed partis stabilized, thus enabling the temperature distribution of steamflowing in the recessed part to be more uniform.

As is apparent from the above description, according to the steam cookerof the invention, a steam cooker that can make a temperaturedistribution in a heating chamber uniform and secure cooking with nouneven heating is realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an external appearance of a steamcooker according to one embodiment of the invention;

FIG. 2 is a perspective view showing an external appearance of the steamcooker with its door opened;

FIG. 3 is a schematic diagram showing the construction of the steamcooker;

FIG. 4( a) is a plan view of a pot of a steam generator of the steamcooker, and FIG. 4( b) is a side view of the pot;

FIG. 5( a) is a side view of the steam generator 40, and FIG. 5( b) is across sectional view taken along line V-V of FIG. 5( a);

FIG. 6 is a control block diagram of the steam cooker;

FIG. 7( a) is a plan view, seen from below, of a steamtemperature-raising device of the steam cooker, and FIG. 7( b) is a sideview of the steam temperature-raising device, seen from a side of steamsupply ports;

FIG. 8( a) is a plan view, seen from below, of a steamtemperature-raising device not having a second steam superheater, andFIG. 8( b) is a side view of the steam temperature-raising device, seenfrom a side of steam supply ports;

FIG. 9( a) is a schematic view showing a steam flow in the steamtemperature-raising device, and FIG. 9( b) is a schematic view showinganother example of a tray-shaped case of the steam temperature-raisingdevice;

FIG. 10 is a schematic view showing a steam flow in another steamtemperature-raising device;

FIG. 11( a) is a view for explaining heat radiation fins of the steamtemperature-raising device of the steam cooker according to theembodiment of the invention, and FIG. 11( b) is a view for explainingheat radiation fins having a wider pitch than that of the heat radiationfins of FIG. 11( a);

FIG. 12 is a front elevational view of the steam cooker with its dooropened; and

FIG. 13 is a view for explaining another example of a heater to be usedin the steam temperature-raising device of the steam cooker.

DETAILED DESCRIPTION OF THE INVENTION

The steam cooker of the invention will be described using examples shownin the drawings.

FIG. 1 is an external perspective view of a steam cooker 1 according toone embodiment of the invention. In the steam cooker, a front upperportion of a rectangular parallelepiped cabinet 10 is provided with anoperation panel 11, and a door 12, which is rotatable around a lower endside of the cabinet, is provided under the operation panel 11. An upperportion of the door 12 is provided with a handle 13, and the door 12 isprovided with a window 14 made of thermal glass.

FIG. 2 is an external perspective view of the steam cooker 1 with thedoor 12 opened. A rectangular parallelepiped heating chamber 20 isprovided in the cabinet 10. The heating chamber 20 has an opening 20 aon its front side facing the door 12, and side surfaces, a bottomsurface and a top surface of the heating chamber 20 are formed ofstainless steel plates. A side of the door 12 facing the heating chamber20 is formed of a stainless steel plate. A heat insulator (not shown) isplaced in the surrounding of the heating chamber 20 and the interior ofthe door 12 to insulate the inside of the heating chamber 20 from theoutside.

A stainless steel-made catch pan 21 is placed at the bottom surface ofthe heating chamber 20, and a stainless steel wire-made rack 24 (shownin FIG. 3) for receiving an object to be cooked is placed on the catchpan 21. Further, side steam outlets 22, 22 of a roughly rectangularshape, which are longitudinally roughly level to each other (only one ofthe openings is shown in FIG. 2), are provided at both lateral sidesurfaces of the heating chamber 20.

FIG. 3 is a schematic view showing the basic construction of the steamcooker 1. As shown in FIG. 3, the steam cooker X includes the heatingchamber 20, a water tank 30 for storing water for steam, a steamgenerator 40 for evaporating water supplied from the water tank 30, asteam temperature-raising device 50 for heating steam from the steamgenerator 40 and a control unit 80 for controlling the steam generator40, the steam temperature-raising device 50 and other devices.

The lattice-like rack 24 is placed on the catch pan 21 placed in theheating chamber 20, and an object 90 to be cooked is placed at a roughlycentral portion of the rack 24.

A connecting portion 30 a provided at the lower side of the water tank30 is connected to a funnel-like receiving port 31 a provided at one endof a first water supply pipe 31. The suction side of a pump 35 isconnected to an end of a second water supply pipe 32, which branches offfrom the first water supply pipe 31 and extends upward, and one end of athird water supply pipe 33 is connected to the discharge side of thepump 35. A water level sensor 36 for the water tank is provided at anupper end portion of a pipe 38 for the water level sensor, which pipebranches off from the first water supply pipe 31 and extends upward.Further, an upper end portion of an air releasing pipe 37 that branchesoff from the first water supply pipe 31 and extends upward is connectedto an exhaust gas duct 65.

The third water supply pipe 33 has an L shape that is bent roughlyhorizontally from a vertically placed portion and an auxiliary tank 39is connected to the other end of the third water supply pipe 33. One endof a fourth water supply pipe 34 is connected to a lower end of theauxiliary tank 39, and the other end of the fourth water supply pipe 34is connected to a lower end of the steam generator 40. One end of adrain valve 70 is connected to the lower end of the steam generator 40,to which the fourth water supply pipe 34 is connected at one endthereof. One end of a drain pipe 71 is connected to the other end of thedrain valve 70, and a water drain tank 72 is connected to the other endof the drain pipe 71. An upper portion of the auxiliary tank 39communicates with air via the air releasing pipe 37 and the exhaust gasduct 65.

Once the water tank 30 has been connected, water rises in the airreleasing pipe 37 until its water level reaches the same water level asthat of the water tank 30. Since a tip of the pipe 38 connected to thewater level sensor 36 for the water tank is sealed, the water level inthe pipe 38 does not rise, but a pressure in a sealed space in the pipe38 for the water level sensor increases from an atmospheric pressure,depending on the water level of the water tank 30. This pressure changeis detected by a pressure detection device (not shown) in the waterlevel sensor 36 for the water tank, whereby the water level in the watertank 30 is detected. Although water level measurement does not requirethe air releasing pipe 37 while the pump 35 is stationary, the airreleasing pipe 37 having an open end is used in order to preventdeterioration of accuracy in the detection of the water level due todirect application of a suction pressure of the pump 35 to the pressuredetection device.

The steam generator 40 has a pot 41, to the lower side of which theother end of the fourth water supply pipe 34 is connected, a heater 42placed in the vicinity of a bottom surface in the pot 41, a water levelsensor 43 placed in the vicinity of the upper side of the heater 42 inthe pot 41, and a steam suction ejector 44 attached to the upper side ofthe pot 41. A fan casing 26 is placed outside an intake opening 25provided at an upper portion of a lateral side of the heating chamber20. Steam in the heating chamber 20 is sucked through the intake opening25 by a blower fan 28 placed in the fan casing 26. The sucked steam issent to an inlet side of the steam suction ejector 44 via a first pipe61 and a second pipe 62. The first pipe 61 is placed roughlyhorizontally, and its one end is connected to the fan casing 26. Thesecond pipe 62 is roughly vertically placed, and its one end isconnected to the other end of the first pipe 61, and the other end ofthe second pipe 62 is connected to the inlet side of an inner nozzle 45of the steam suction ejector 44.

The steam suction ejector 44 is provided with an outer nozzle 46 thatcovers an outer side of the inner nozzle 45, and the discharge side ofthe inner nozzle 45 communicates with an internal space of the pot 41.The discharge side of the outer nozzle 46 of the steam suction ejector44 is connected to one end of a third pipe 63 and a steamtemperature-raising device is connected to the other end of the thirdpipe 63.

The fan casing 26, the first pipe 61, the second pipe 62, the steamsuction ejector 44, the third pipe 63 and the steam temperature-raisingdevice 50 form an external circulation passage 60. One end of adischarge passage 64 is connected to a discharge port 27 provided in alower portion of the lateral side of the heating chamber 20, and theother end of the discharge passage 64 is connected to one end of theexhaust gas duct 65. The other end of the exhaust gas duct 65 isprovided with an exhaust gas outlet 66. A radiator 69 is outwardlyfitted to the exhaust gas duct 65 side of the discharge passage 64. Aconnection portion of the first pipe 61 and the second pipe 62 isconnected to the exhaust gas duct 65 through an exhaust gas passage 67.At the connection side with the first and second pipes 61, 62, theexhaust gas passage 67 is provided with a damper 68 that opens/closesthe exhaust gas passage 67.

The steam temperature-raising device 50 includes a tray-shaped case 51placed with its opening downward on a ceiling side at a central portionof the heating chamber 20, a first steam superheater 52 placed in thetray-shaped case 51, and a second steam superheater 53 placed in thetray-shaped case 51. A bottom of the tray-shaped case 51 is formed of ametallic ceiling panel 54 serving as a ceiling plane of the heatingchamber 20. The ceiling panel 54 is formed with a plurality of ceilingsteam outlets 55. Both upper and lower surfaces of the ceiling panel 54give a dark color by coating and the like. The ceiling panel 54 may alsobe formed of a metal material that turns into a dark color by repetitiveuse or a dark ceramic molded product.

One end of each of steam supply passages 23 (in FIG. 3, only one of themis shown), which extend to the left and right sides of the heatingchamber 20, is individually connected to the steam temperature-raisingdevice 50. The other end of each of the steam supply passages 23 extendsdownward along the side surfaces of the 5 heating chamber 20 and isconnected to side steam outlets 22, which are provided in a lowerposition of the lateral side of the heating chamber 20,

Next, the steam generator 40 will be described in detail with referenceto FIGS. 4, 5.

First, FIG. 4( a) is a plan view, seen from above, of the pot 41 of thesteam generator 40, and FIG. 4( b) is a side view of the pot 41.

As shown in FIGS. 4( a), (b), the pot 41 includes a cylinder portion 41a which has, in its horizontal plan view, a roughly rectangular shape, abottom portion 41 b provided on the lower side of the cylinder portion41 a and formed of an inclined plane that is gradually lowered toward acenter portion of the bottom portion, and a water supply port 41 cprovided at a roughly center portion of the bottom portion 41 b.Although the vertical to horizontal ratio of the planar shape of the pot41 is 1:2.5, what is required of the planar shape is that the planarshape is an elongated shape, namely a rectangular or elliptic shape.Preferably, however, the vertical to horizontal ratio in the case of therectangular shape is 1:2, more preferably 1:2.5, and most preferably 1:3or less.

The heater 42 is placed in the vicinity of the bottom portion 41 b inthe pot 41. The heater 42 is constructed of a first steam generationheater 42A that is a U-shaped sheath heater having a larger pipediameter and a second steam generation heater 42B that is a U-shapedsheath heater having a smaller pipe diameter, which is placed inside thefirst steam generation heater 42A and roughly on the same plane as thefirst generation heater 42A. The heater 42 is placed adjacent tosidewalls of the cylinder portion 41 a of the pot 41. A minimum distancebetween an outer edge of the heater 42 and the sidewalls of the cylinderportion 41 a is set to 2 mm to 5 mm. A lowermost portion of the heater42 is placed adjacent to the bottom portion 41 b of the pot 41. Aminimum distance between a lowermost portion of the heater 42 and thebottom portion 41 b of the pot 41 is set to 2 mm to 5 mm.

In this embodiment, a 700 W sheath heater having a larger pipe size isused for the first steam generation heater 42A, while a 300 W sheathheater having a smaller pipe size is used for the second steamgeneration heater 42B. The first steam generation heater 42A has acurved portion 42Aa that has a roughly semicircular arc shape, and twolinear portions 42Ab, 42Ac that extend roughly parallel from both endsof the curved portion 42Aa. The second steam generation heater 42B has acurved portion 42Ba that has a generally semicircular arc shape, and twolinear portions 42Bb, 42Bc that extend roughly parallel from both endsof the curved portion 42Ba. The curved portion 42Aa of the first steamgeneration heater 42A has a minimum curvature radius r1, which isdetermined by the sheath heater having a larger pipe size to be used,while the curved portion 42Ba of the second steam generation heater 42Bhas a minimum curvature radius r2 (<r1), which is determined by thesheath heater having a smaller pipe size to be used.

A water level sensor 43 is placed in the vicinity of the upper side ofthe heater 42 in the pot 41 and at a sidewall on the side of anon-heating portion (region C of FIG. 4( a)) inside the second steamgeneration heater 42B. In the pot 41, a partition plate 47 having asquare cornered U-shape in cross section, which surrounds the waterlevel sensor 43, is provided. The partition wall 47 and the sidewall inthe pot 41 form a casing having a rectangular shape in cross section. Alower end of the partition plate 47 is located on the upper side of thebottom portion 41 b of the pot 41 and beneath the lowermost portions ofthe first and second steam generation heaters 42A, 42B. On the otherhand, an upper end of the partition plate 47 is set at a level that istwice or more of a height from the lowermost portion of the heater 42 toan attaching position of the water level sensor 43. Further, atemperature sensor 48 is placed at a sidewall opposite to the waterlevel sensor 43 in the pot 41.

The water level sensor 43 is a self-heating thermistor. In water, atemperature ranging from about 100° C. to 140° C. is detected dependingon a water temperature ranging from about 20° C. to 100° C., while, inair, a temperature ranging from about 140° C. to 150° C. is detected.Based on the water temperature detected by the temperature sensor 48,the temperature detected by the water level sensor 43 is determined,whereby the presence or absence of water, namely whether or not water ispresent at the attaching position of the water level sensor 43 isdetermined.

FIG. 5( a) is a side view of the steam generator 40, and FIG. 5( b) is across sectional view taken along line V-V of FIG. 5( a).

As shown in FIGS. 5( a), (b), the steam suction ejector 44 is attachedin a manner so as to cover an upper side opening of the pot 41, which isinternally provided with the first and second steam generation heaters42A, 42B. A fluid (steam) flowing in from an inlet 45 a of the innernozzle 45 is discharged from the opening 45 b of the inner nozzle 45 andthen discharged from the opening 46 a of the outer nozzle 46. At thistime, since the discharge side of the inner nozzle 45 communicates withan internal space of the pot 41, saturated steam generated in the pot41, which is led to the opening 46 a side of the outer nozzle 46, isdischarged from the opening 46 a of the outer nozzle 46 together withsteam discharged from the opening 45 b of the inner nozzle 45. That is,saturated steam with a temperature of 100° C. and a pressure of 1 atm.(i.e., 1013.25 hPa), which is generated by boiling water in the pot 41,is sucked into a circulating airflow that passes the externalcirculation passage 60 (shown in FIG. 3). By the structure of the steamsuction ejector 44, saturated steam is immediately sucked up. Since nopressure is applied in the steam generator 40, discharge of saturatedsteam is not hindered.

Next, a control block diagram of the steam cooker 1 shown in FIG. 6 willbe described.

As shown in FIG. 6, connected to the control unit 80 are the blower fan28, the first steam superheater 52, the second steam superheater 53, thedamper 68, the drain valve 70, the first steam generation heater 42A,the second steam generation heater 42B, the operation panel 11, thewater level sensor 36 for the water tank, the water level sensor 43, atemperature sensor 81 for detecting a temperature in the heating chamber20 (shown in FIG. 3), a humidity sensor 82 for detecting a humidity inthe heating chamber 20, and the pump 35.

The control unit 80 has a microcomputer and an input/output circuit.Based on detection signals received from the water level sensor 36 forthe water tank, the water level sensor 43, the temperature sensor 81,and the humidity sensor 82, the control unit 80 controls the blower fan28, the first steam superheater 52, the second steam superheater 53, thedamper 68, the drain valve 70, the first steam generation heater 42A,the second steam generation heater 42B, the operation panel 11, and thepump 35 in accordance with a predetermined program.

In the steam cooker 1 with the above construction, a power switch (notshown) on the operation panel 11 is pushed to power up, and a cookingoperation is started by an operation of the operation panel 11. Then,the control unit 80 first closes the drain valve 70, and starts tooperate the pump 35 in a state in which the exhaust gas passage 67 isclosed by the damper 68. Water is supplied by the pump 35 from the watertank 30 into the pot 41 of the steam generator 40 via the first throughfourth water supply pipes 31-34. Then, when the water level sensor 43detects that the water level in the pot 41 has reached a predeterminedlevel, the control unit 80 stops the pump 35 to stop water supply.

Next, the first and second steam generation heaters 42A, 42B are turnedon, and a predetermined amount of water stored in the pot 41 is heatedby the first and second steam generation heaters 42A, 42B.

Subsequently, simultaneously with turn-on of the first and second steamgeneration heaters 42A, 42B, or when the water temperature in the pot 41has reached a predetermined temperature, the blower fan 28 is turned on,and, at the same time, the first steam superheater 52 is turned on.Then, the blower fan 28 sucks air including steam) in the heatingchamber 20 through the intake openings 25 and sends the air (includingsteam) to the external circulation passage 60. Since a centrifugal fanis used as the blower fan 28, it is possible to generate a higherpressure than with a propeller fan. Furthermore, the centrifugal fanused as the blower fan 28 is rotated at a high speed by a DC motor,whereby a flow rate of the circulating airflow can be highly increased.

Next, when water in the pot 41 of the steam generator 40 boils,saturated steam is generated. The generated saturated steam merges intothe circulating airflow that goes through the external circulationpassage 60, at the steam suction ejector 44. Steam ejected from thesteam suction ejector 44 flows into the steam temperature-raising device50 at a high speed via the third pipe 63.

Steam flowing into the steam temperature-raising device 50 is heated bythe first steam superheater 52 to be superheated steam of about 300° C.(which varies depending on the type of cooking). A part of thesuperheated steam is jetted downward into the heating chamber 20 fromthe plurality of ceiling steam outlets 55 provided in the lower ceilingpanel 54. Another part of the superheated steam is jetted from the sidesteam outlets 22 in both of the lateral sides of the heating chamber 20via the steam supply passages 23, which extend to the left and rightsides of the steam temperature heating device 50.

Thereby, superheated steam jetted from the ceiling side of the heatingchamber 20 is vigorously supplied to the object 90 side. Also,superheated steam jetted from the left and right lateral sides of theheating chamber 20 is supplied in a manner so as to wrap the object 90,while going up from the lower side of the object 90, after collidingwith the catch pan 21. Thereby, a convective superheated steam flow, inwhich steam blows down into a central portion and ascends in its outerside, is generated in the heating chamber 20. The convective superheatedsteam flow repeats a cycle of being sucked into the intake openings 25,passing the external circulation passage 60 and returning to the insideof the heating chamber 20 again.

In this manner, by forming a convective superheated steam flow in theheating chamber 20, it becomes possible to jet superheated steam, whichis sent from the steam temperature-raising device 50, from the ceilingsteam outlets 55 and the side steam outlets 22 so that it efficientlycollides with the object 90, while maintaining uniform temperature,humidity distribution in the heating chamber 20. Then, collision ofsuperheated steam heats the object 90. At this time, superheated steamin contact with a surface of the object 90 heats the object 90 also byreleasing latent heat that is generated when building up condensation onthe surface of the object 90. Thereby, a large quantity of heat canuniformly be imparted to the entire surface of the object 90 surely andpromptly. Therefore, uniform cooking that secures a good finish can berealized.

In the cooking operation, an amount of steam in the heating chamber 20increases with a lapse of time, and an excess amount of steam isdischarged from the exhaust gas outlet 66 via the discharge port 27, thedischarge passage 64 and the exhaust gas duct 65. At this time, aradiator 69 provided on the discharge passage 64 cools steam passing thedischarge passage 64 to form condensation, whereby steam is preventedfrom being discharged to the outside as such. Water condensed by theradiator 69 within the discharge passage 64 runs down the dischargepassage 64, is led to the catch pan 21, and disposed of together withwater generated by cooking after completion of the cooking.

After completion of the cooking, the control unit 80 displays a messageof completion of the cooking on the operation panel 11, and a sound israised by a buzzer (not shown) provided on the operation panel 11.Thereby, a user who has noticed completion of the cooking opens the door12. Then, the control unit 80 opens the damper 68 immediately after asensor (not shown) detects opening of the door 12. Thereby, the firstpipe 61 of the external circulation passage 60 communicates with theexhaust gas duct 65 via the exhaust gas passage 67, so that steam in theheating chamber 20 is discharged by the fan 28 from the exhaust gasoutlet 66 via the intake openings 25, the first pipe 61, the exhaust gaspassage 67 and the exhaust gas duct 65. The operation of the damper isthe same even if the user opens the door 12 while cooking Therefore, theuser can safely take out the object 90 from the inside of the heatingchamber 20 without being exposed to steam.

The heater 42 is placed in the vicinity of the bottom portion 41 b inthe pot 41 of the steam generator 40 as well as roughly on the samelevel, whereby the water level of water supplied into the pot 41 can beset to a range from the bottom portion 41 b of the pot 41 to a littleabove the upper side of the heater 42. Therefore, by setting the waterlevel in the pot 41 to a range from the bottom portion 41 b of the pot41 to a little above the upper side of the heater 42, and making thewater level as low as possible, the amount of water in the pot 41, whichis heated by the heater 42, can be made as small as possible, and startof steam generation by the steam generator 40 can be quickened. Byquickening the start of steam generation by the steam generator 40, thestart of superheated steam generation can be quickened, so that timerequired for cooking can be reduced. In particular, in cooking for thefirst time after stopping the operation for a long time, start ofgeneration of superheated steam supplied into the heating chamber 20 canbe quickened without requiring preheating while it is stopped. Thus, aneffect of reducing the cooking time is noticeable.

The heater 42 is placed in the pot 41 whose planar shape is an elongatedshape (a roughly rectangular shape in this embodiment), and the sheathheaters (42A, 42B) used as the heater 42 are placed in a manner so as tobe along the sidewalls of the pot 41, whereby an area taken up by aregion surrounded by an outer edge of the heater 42 is reduced, thusmaking it possible to increase heater power relative to a floor area (oran area at the water level) taken up by the heater in the pot 41, aswell as possible to reduce a planar area of the pot 41. Therefore, byincreasing the heater power relative to the floor area (or the area atthe water level) taken up by the heater in the pot 41, and reducing theplanar area of the pot 41 so that the amount of water is reduced, thesteam generation by the steam generator 40 can be quickened more.

In the first steam generation heater 42A that is a U-shaped sheathheater having a larger pipe size and the second steam generation heater42B that is a U-shaped sheath heater having a smaller pipe size, whichis placed inside the first generation heater 42A and roughly at the samelevel as the first generation heater 42A, the radius of curvature of thecurved portion 42Ba is made to be the minimum. The radius of curvatureis determined by the pipe size of the sheath heater and the like Then,if the power is applied to the heater in the same condition, the areataken up by the region surrounded by the outer edge of the heater 42 canbe reduced so that the heater power relative to the area (or the area atthe water level) taken up by the heater in the pot 41 is made highest.By making the heater power relative to the area (or the area at thewater level) taken up by the heater in the pot 41 high, start of steamgeneration by the steam generator can be quickened more. Energization ofthe first steam generation heater 42A having a high power (700 W) andenergization of the second steam generation heater 42B having a lowpower (300 W) is switched by the control unit 80, thereby making itpossible to control the power applied for steam generation depending ona combination of the heaters. This enables the generation of steamdepending on the type of cooking.

FIG. 7( a) is a plan view, seen from below, of the steamtemperature-raising device 50 of the steam cooker, and FIG. 7( b) is aside view of the steam temperature-raising device seen from the side ofsteam supply ports. In the steam temperature-raising device 50, as shownin FIGS. 7( a), (b), the first steam superheater 52 that is a high power(1000 W) sheath heater having a larger pipe size and the second steamsuperheater 53 that is a low power (300 W) sheath heater having asmaller pipe diameter, or size are placed in the tray-shaped case 51having a recessed part 51 a whose planar shape is a roughly pentagonalshape. The second steam superheater 53 has a higher power density perunit surface area than that of the first steam superheater 52. Althoughnot shown in FIGS. 7( a), (b), the opening of the recessed part 51 a ofthe tray-shaped case 51 is covered by the metallic ceiling panel 54(shown in FIG. 3) provided on the ceiling plane of the heating chamber20.

The recessed part 51 a of the tray-shaped case 51 has a first sidewall91 to which steam supply pipes 94A, 94B, 94C are connected, a secondsidewall 92A which is adjacent to one side of the first sidewall 91through a round portion 105A and is roughly perpendicular to the firstsidewall 91, a third sidewall 92B which is adjacent to the other side ofthe first sidewall 91 through a round portion 105B and is roughlyperpendicular to the first sidewall 91 and parallel to the secondsidewall 92A, a fourth sidewall 93A which is adjacent to the secondsidewall 92A through a round portion 106A and forms a blunt angle withthe second sidewall 92A, and a fifth sidewall 93B which is adjacent tothe third sidewall 92B through a round portion 106B, forms a blunt anglewith the third sidewall 92B, and also forms a blunt angle with thefourth sidewall 93A. The fourth sidewall 93A and the fifth sidewall 93Bare adjacent to each other through a round portion 107. In thetray-shaped case 51, the round portions 105A, 106A, 106B, 107 that arecorner portions of the recessed part 51 a having a curved surface areformed by drawing.

In the tray-shaped case 51, the side of the first sidewall 91 to whichthe steam supply pipes 94A, 94B, 94C are connected corresponds to theback side (FIG. 7( a) on the right) of the steam cooker 1, while theside of the forth sidewall 93A and the fifth sidewall 93B corresponds tothe front side (FIG. 7( a) on the left) of the steam cooker 1n The steamsupply pipe 94A having a steam supply port 95A is connected to a roughlycentral portion of the first sidewall 91, and the steam supply pipes948, 94C having steam supply ports 95B, 95C are connected on both sidesof the steam supply pipe 94A at predetermined intervals. Steam outlets101A, 102A, 103A, 104A are provided at predetermined intervals in thesecond sidewall 92A from the front side toward the back side, and atpositions in the third sidewall 92B opposite to the steam outlets101A-104A, steam outlets 101B, 102B, 103B, 104B are provided. The steamoutlets 101A-104A, and the steam outlets 101B-104B are connected to thesteam supply passage 23 shown in FIG. 3. The discharge side of the steamsuction ejector 44 is connected to the inlet port side of the steamsupply pipes 94A, 948, 94C via the third pipe 63 shown in FIG. 3.

A first and a second non-heating portion 52 b, 52 c of the first steamsuperheater 52 pass through the sidewall 91 and fixed at the outside ofthe steam supply pipes 94A, 94C. Electric wirings (not shown) areconnected to leading ends of the first and the second non-heatingportion 52 b, 52 c of the first steam superheater 52. The first steamsuperheater 52 has a planar shape roughly symmetrical with respect tothe center line L of the flow of steam flowing in from the steam supplyports 95A, 95B, 95C, and includes the two non-heating portions 52 b, 52c placed parallel to the center line L at a predetermined interval, tworoughly U-shaped heating portions 52 a-1, 52 a-2 which are connected, atone end thereof, to the leading ends of the non-heating portions 52 b,52 c and which are each curved toward the center of the recessed part 51a, and a roughly U-shaped third heating portion 52 a-3 which connectsthe two first and second heating portions 52 a-1, 52 a-2. Spiral heatradiation fins 56 are provided around the first to third heatingportions 52 a-1 to 52 a-3 and a part of the first and second non-heatingportions 52 b, 52 c of the first steam superheater 52.

Non-heating portions 53 b, 53 c at both ends of the second steamsuperheater 53 pass through the sidewall 91 and are fixed between thesteam supply pipes 94A and 94B and between the steam supply pipes 94Band 94C, respectively. Electric wirings (not shown) are connected toleading ends of the non-heating portions 53 b, 53 c of the second steamsuperheater 53. A heating portion 53 a of the second steam superheater53 has a circular shape and both ends of the circular heating portion 53have a shape continuous with the non-heating portions 53 b, 53 c. Thesecond steam superheater 53 has a planar shape roughly symmetrical withrespect to the center line L of the flow of steam flowing in from thesteam supply ports 95A, 95B, and 95C.

A part of steam in the recessed part 51 a of the tray-shaped case 51blows out into the heating chamber 20 from the steam outlets 101A-104A,101B-104B, which are provided in the second and third sidewalls 92A, 92Bfacing each other across the center line L and on the side (front side)opposite from the steam supply ports 95A, 95B, 95C, and also from theside steam outlets 22A, 22B (shown in FIG. 12) via the steam supplypassage 23 (shown in FIG. 3).

FIG. 8( a) shows a plan view, seen from below, of a steamtemperature-raising device not having a second steam superheater, andFIG. 8( b) shows a side view of the steam temperature-raising deviceseen from the side of steam supply ports. The steam temperature-raisingdevice 150 has the same construction as that of the steamtemperature-raising device shown in FIGS. 7( a) and 7(b) except for nothaving the second steam superheater and the shape of the first steamsuperheater, and thus corresponding components are denoted by the samenumerals and their description is omitted. In FIG. 8( a), the referencenumeral 151 denotes a tray-shaped case not provided with a fitting placefor a second steam superheater, the reference numeral 152 denotes afirst steam superheater, the reference numerals 105A, 105B, 106A, 106B,and 107 denote round portions.

Next, the steam flow at the steam temperature-raising device 50 will bedescribed using FIG. 9( a).

As shown in FIG. 9( a), steam supplied from the steam generator 40(shown in FIG. 3) passes the steam supply ports 95A, 95B, 95C on theupper side in the figure (the back side) and flows downward in thefigure (the front side) into the tray-shaped case 51. For example, iffocusing on a steam flow R1 flowing in from the steam supply port 95B,the steam flow R1 is divided into a fourth sidewall 93A side and a fifthsidewall 933 side to be branch flows R2A and R2B, respectively, in thevicinity of the round portion 107 of the recessed part 51 a of thetray-shaped case 51. A part of the branch flow R2A flows sideways alongthe fourth sidewall 93A, turns in the vicinity of the round portion 106Aso as to flow along the second sidewall 92A, and then turns inward inthe round portion 105A to merge into the flow R1 again. Similarly, apart of the branch flow R2B flows sideways along the fifth sidewall 93B,turns in the vicinity of the round portion 106B so as to flow along thethird sidewall 92B, and turns inward in the round portion 105B to mergeinto the flow R1 again Further, steam flowing in from the other steamsupply ports 95A, 95C also flows along the steam flow R1 flowing in fromthe steam supply port 95B.

In this manner, superheated steam is generated by heating steam in therecessed part 51 a of the tray-shaped case 51 by means of the first andsecond steam superheaters 52, 53. The thus generated superheated steamblows out from the ceiling steam outlets 55 (shown in FIG. 3) and thesteam outlets 101A-104A, 101B-104B.

In the steam temperature-raising device 50 of the above embodiment, theplanar shape of the recessed part 51 a of the tray-shaped case 51 ismade in a roughly pentagonal shape having three sides forming a U-shape,and two sides that form a V-shape projecting outward, which are iscontinuous with both ends of the U-shape of the three sides. However,the planar shape of the recessed part of the tray-shaped case is notlimited to this. For example, as shown in FIG. 9( b), a shape havingthree sides forming a U-shape and a wall surface 96 with an arc-shapedouter periphery that is continuous with both ends of the U-shape of thethree sides may be applied.

Contrary to this, for example, in the case where the tray-shaped case ofthe steam temperature-raising device has a shape in which front cornerportions on both sides thereof have an acute angle as shown in FIG. 10,steam flows into a tray-shaped case 251 from the steam supply ports 95A,95B, 95C on the upper side of the figure (the back side) to the lowerside of the figure (the front side) For example, if focusing on a steamflow R11 that flows in from the steam supply port 95B, the steam flowR11 is divided on the opposite side of the steam supply port 95B to bebranch flows R12A and R12B. At this time, steam accumulations SA, SB areformed at the acute-angled corner portions, and due to the steamaccumulations SA, SB, a steam temperature distribution in thetray-shaped case 251 becomes non-uniform.

FIG. 11( a) shows a view for describing heat radiation fins of the steamtemperature-raising device of the steam cooker of the invention. Thisshows parts of the first and second heating portions 52 a-1, 52 a-2,which are parallel to each other, of the first steam superheater 52 inthe vicinity of the first sidewall 91 of the tray-shaped case 51 (shownin FIGS. 7( a), (b)). Since the spiral heat radiation fins 56 areprovided in the same winding direction around the first steamsuperheater 52, inclined planes of the heat radiation fins 56 areinclined in the same direction. Therefore, for example, influence of theinclined planes of the heat radiation fins 56 on steam flowing from theupper side to the lower side in the figure through the center of thefirst and second heating portions 52 a- 1, 52 a-2, which are parallel toeach other, of the first steam superheater 52 shown in FIG. 11( a)varies. However, in this embodiment, the fin pitch of the spiral heatradiation fins 56 that are provided around the first steam superheater52 is set to 10 mm, whereby the distribution of the degree of influence(disturbance or resistance loss) of the heat radiation fins 56 on thesteam flow blowing out from the steam supply ports 94A, 94B, 94C (shownin FIG. 9) is made symmetrical with respect to the center line L ofsteam.

As shown in FIG. 11( b), in the case where heat radiation fins 57 havinga wider fin pitch than that of FIG. 11( a) are provided around the firststeam superheater 52, the influence of the heat radiation fins 57 on thesteam flow blowing out from the steam supply ports 94A, 94B, 95C (shownin FIG. 9) varies between the left and right sides, so that the steamflow in the recessed part 51 a of the tray-shaped case 51 is disturbedand not stabilized. Consequently, it becomes impossible to make thetemperature distribution uniform.

FIG. 12 is a front elevational view of the steam cooker with its dooropened. The intake openings 25 are placed in an upper corner of theback, and the circular panel 54 having the plurality of ceiling steamoutlets 55 is attached to the center of the ceiling side of the heatingchamber 20. Further, the side steam outlets 22A, 22B, from which steamfrom the steam temperature-raising device 50 blows out, are placed in alower position of the left and right lateral sides of the heatingchamber 20. The water tank 30 is placed on the observer's left of theheating chamber 20.

In this manner, according to the steam cooker with the aboveconstruction, the planar shapes of the recessed part 51 a of thetray-shaped case 51 and the first steam superheater 52 placed in therecessed part 51 a thereof are made roughly symmetrical with respect tothe center line L of the flow of steam flowing in from the steam supplyports 95A, 95B, 95C, whereby steam flow in the recessed part 51 a is notbiased or deviated, the temperature distribution thereof is madeuniform, and the temperature distribution of steam supplied into theheating chamber 20 from the ceiling steam outlets 55 of the ceilingpanel 54 of the heating chamber 20 can be made uniform.

Further, the fin pitch of the spiral heat radiation fins 56, which arewound around the first steam superheater 52 placed in the recessed part51 a of the tray-shaped case 51, is set to 10 mm or less, whereby thedegree of influence (disturbance or resistance loss) on the steam flowblowing out from the steam supply ports 95A, 95B, 95C can be maderoughly symmetrical with respect to the center line L. Consequently, thetemperature distribution of steam in the recessed part 51 a is made moreuniform, and the temperature distribution of steam supplied into theheating chamber 20 from the ceiling steam outlets 55 of the ceilingpanel 54 of the heating chamber 20 can be made uniform. Therefore, thetemperature distribution in the heating chamber 20 can be made uniform,which makes it possible to perform uniform cooking.

By providing the steam outlets 101A-104A, 101B-10 104B in the second andthe third sidewalls of the recessed part 51 a, respectively, which faceeach other across the center line L, and on the opposite side of thesteam supply ports 95A, 95B, 95C, and arranging the steam outlets101A-104A, 101B-104B in the recessed part 51 a so that they are roughlysymmetrical with respect to the center line L, the amount, flow rate andtemperature distribution of steam blowing sideways to the left or rightfrom the inside of the recessed part 51 a via the steam outlets101A-104A, 101B-104B, can be made uniform. Thus, bias or unevenness inthe temperature distribution of steam supplied sideways into the heatingchamber 20 via the steam supply passage 23 (shown in FIG. 3) can bereduced, so that the temperature distribution in the heating chamber 20can be made more uniform.

Even if the planar shape of the recessed part of the tray-shaped caseand the planar shape of the heater 50 are not symmetrical, by providingthe plurality of steam outlets for supplying steam sideways into theheating chamber in both of the sidewalls adjacent to the sidewallprovided with the steam supply ports of the recessed part of thetray-shaped case on the opposite side of the steam supply ports, thetemperature distribution of steam blowing outward to both sides via theplurality of steam outlets can be made uniform.

Since the fourth and fifth sidewalls 93A, 93B of the recessed part 51 aof the tray-shaped case 51 are inclined with respect to a plane roughlyperpendicular to the center line L of the steam flow flowing in from thesteam supply ports 95A, 95B, 95C, when steam flowing into the recessedpart 51 a collides with the fourth and fifth sidewalls 93A, 93B to bedivided into left and right side branches, the steam branch flows aremade smooth, and generation of steam accumulation and the like causinguneven temperature distribution is suppressed, so that the temperaturedistribution of steam that flows in the recessed part 51 a can be madeuniform.

In the roughly pentagonal recessed part 51 a of the tray-shaped case 51,the two sides that are continuous with both ends of the U-shape of thethree sides and are directed outward to form a V-shape serve as thefourth and fifth sidewalls 93A, 93B, which are inclined with respect tothe plane roughly perpendicular to the center line L. Thereby, whensteam flowing into the recessed part 51 a of the tray-shaped case 51,whose planar shape is symmetrical with respect to the center line L,collides with the fourth and fifth sidewalls 93A, 94B and is dividedinto the left and right side branches, the steam branch flows are madesmooth, generation of steam accumulation and the like, which causesuneven temperature distribution, is suppressed, and the temperaturedistribution of steam flowing in the recessed part 51 a can be made moreuniform.

As shown in FIG. 9( b), the planar shape of the recessed part 51 a ofthe tray-shaped case 51 may be a shape having three sides forming aU-shape, and an arc-shaped outer periphery curved outward and connectingwith both ends of the U-shape of the three sides. In this case, thearc-shaped outer periphery curved outward serves as the wall 96 inclinedwith respect to the plane perpendicular to the center line L. Thereby,when steam flowing into the recessed part 51 a from the steam supplyports 95A, 95B, 95C collides with the wall 96 having the arc-shapedouter periphery and is divided into the left and right side branches,the steam branch flows are made smooth, and generation of steamaccumulation, which causes uneven temperature distribution, issuppressed, so that the temperature distribution of steam that flows inthe recessed part 51 a can be made more uniform.

Further, the round portions 105A, 105B, 106A, 106B, 107 having a curvedsurface are provided at the corners of the recessed part 51 a of thetray-shaped case 51 so that adjacent sidewalls are smoothly continuous,whereby steam flowing into the recessed part 51 a flows along thesidewalls of the recessed part 51 a smoothly. Therefore, the steam flowin the recessed part 51 a is stabilized, and the temperaturedistribution of steam flowing in the recessed part 51 a is made moreuniform.

As shown in FIG. 7( a), because the heat radiation fins 56 are woundaround the first to third heating portions 52 a-1 to 52 a-3 and also apart of the first and second non-heating portions 52 b, 52 c, heattransferred from the side of the first, second heating portion 52 a-1,52 a-2 to the side of the first, second non-heating portion 52 b, 52 cof the first steam superheater 52 is radiated through the heat radiationfins 56 on the side of the non-heating portion 52 b, 52 c. Therefore,the first, second non-heating portion 52 b, 52 c is prevented fromreaching a high temperature due to superheat. Thus, a temperature risein the non-heating portion 52 b, 52 c of the first steam superheater 52,to which electric wiring is connected, can be suppressed, and highreliability can be obtained.

Since the connection portions between the first and second heatingportion 52 a-1, 52 a-2 to the first and second non-heating portion 52 b,52 c of the first steam superheater 52 are located in positions wheresteam flowing in from the steam supply ports 95A, 95B, 95C collidesagainst the vicinity of the connection portions, steam having a lowertemperature than that of steam superheated by the first steamsuperheater 52 is supplied through the steam supply ports 95A, 95C tothe connection portions between the first and second heating portions 52a-1, 52 a-2 and the first and second non-heating portions 52 b, 52 c ofthe first steam superheater 52. Therefore, heat transferred from thefirst, second heating portions 52 a-1, 52 a-2 to the first and secondnon-heating portions 52 b, 52 c of the first steam superheater 52 can beradiated by the low-temperature steam through the heat radiation fins 56on the side of the first and second non-heating portions 52 b, 52 c, sothat a temperature rise in the non-heating portions 52 b, 52 c, to whichelectric wiring is connected, can be suppressed effectively. Further,the connection portions of the first and second heating portions to thefirst and second non-heating portions of the first steam superheater maybe placed at positions where steam flowing in from the steam supplyports directly collides against the connection portions.

Of the first steam superheater 52 having a high power and the secondsteam superheater 53 having a low power, the high-power first steamsuperheater 52 is provided with the heat radiation fins 56 around thefirst to third heating portions 52 a-1 to 52 a-3 and part of thenon-heating portions 52 b, 52 c of, whereby heat transferred from thefirst, second heating portion 52 a-1, 52 a-2 with a high calorific powerto the first, second non-heating portion 52 b, 53 c side of the firststeam superheater 52 can be radiated through the heat radiation fins 56on the side of the first, second non-heating portion 52 b, 52 c, so thata temperature rise of the non-heating portion of the heater, to whichelectric wiring is connected, can be reduced more effectively.

Furthermore, the first and second steam superheaters 52, 53 are placedin the recessed part 51 a of the tray-shaped case 51 of the steamtemperature-raising device 50 such that the heat generation density perunit volume of a space in the vicinity of the steam supply ports 95A,95B, 95C is increased. Therefore, low-temperature steam flowing in fromthe steam supply ports 95A, 95B, 95C collides with the first and secondsuperheaters 52, 53, which provide a region having a high heatgeneration density per unit volume, and the low-temperature steam isthen heated, so that the temperature distribution in the entire recessedpart 51 a of the tray-shaped case 51 is made uniform. Thus, thetemperature distribution of steam supplied from the ceiling steamoutlets 55 into the heating chamber 20 can be made uniform Accordingly,the temperature distribution in the heating chamber 20 can be madeuniform enabling even cooking.

Of the first and second superheaters 52, 53 having different powerdensities per unit surface area, the second superheater 53 having ahigher power density per unit surface area is placed in the vicinity ofthe steam supply ports 95A, 95B, 95C, whereby low-temperature steamflowing in from the steam supply ports 95A, 95B, 95C is heated by thesecond steam superheater having the higher power density per unitsurface area. Therefore, the start of steam temperature rise can beaccelerated, so that a reduction in cooking time is ensured and thetemperature distribution in the entire recessed part 51 a of thetray-shaped case 51 can be made uniform more effectively.

Of the first and second superheaters 52, 53 with different powerdensities per unit surface area and having a planar shape that issymmetrical with respect to the center line L of the steam flow enteringfrom the steam supply ports 95A, 95B, 95C, the second steam superheater53 having a high power density per unit surface area is placed inside,while the first steam superheater 52 having a low power density per unitsurface area is placed outside, whereby low-temperature steam flowing infrom the steam supply ports 95A, 95B, 95C is heated by the second steamsuperheater 53 having a high power density per unit surface area, whichis placed inside, and, in its outside, steam is heated by the firststeam superheater 52 having a low power density per unit surface area.Therefore, the temperature distribution in the entire recessed part 51 aof the tray-shaped case 51 can be made uniform more effectively.

Due to the use of the first and second steam superheaters 52, 53 havinga planar shape that is symmetrical with respect to the center line L ofthe steam flow entering from the steam supply ports 95A, 95B, 95C, steamflow is not biased toward the left or right side so that the temperaturedistribution in the recessed part 51 a of the tray-shaped case 51 can bemade uniform effectively.

The first steam superheater 52 has the two first and second non-heatingportions 52 b, 52 c that are spaced from each other and placed roughlyparallel to the center line L, the two roughly U-shaped first and secondheating portions 52 a-1, 52 a-2 which are connected, at one end thereof,to leading ends of the first and second non-heating portions 52 b, 52 c,respectively, and which are each curved toward the center of therecessed part 51 a into a U shape, and the roughly U-shaped thirdheating portion 52 a-3 that connects between the other ends of the firstand second heating portions 52 a-1, 52 a-2, and the first steamsuperheater 52 has a planar shape that is symmetrical with respect tothe center line of the steam flow entering from the steam supply ports95A, 95B, 95C. Thus, steam flow in the recessed part 51 a is not biased,so that the temperature distribution in the entire recessed part 51 a ofthe tray-shaped case 51 can be made uniform effectively.

In the above embodiment, the heater 42 is used, which has the firststeam generation heater 42A that is a U-shaped sheath heater having alarger pipe size and the second steam generation heater 42B that is aU-shaped sheath heater having a smaller pipe size, which is placedinside the first steam generation heater 42A. The shape of the heater isnot limited to this. However, the heaters are preferably placed roughlyon the same level in the vicinity of the bottom portion in the pot.

In the above embodiment, the first steam superheater 52 (shown in FIG.7) as a planar heater is used for the steam temperature-raising device50. The shape of the heater is not limited to the above-described one,and any heater may be used as long as it has a planar shape that isroughly symmetrical with respect to the center line L of the steam flowflowing in from the steam supply ports.

For example, as shown in FIG. 13, a heater 58 placed in the recessedpart 51 a of the tray-shaped case 51 may be used. The heater 58 has alinear portion 58 a, a semi-circular curved portion 58 b, a linearportion 58 c, a semi-circular curved portion 58 d, a linear portion 58e, a semi-circular curved portion 58 f, and a linear portion 58 g.

One end (on the side of the non-heating portion) of the linear portion58 a is inserted through the first side wall 91 of the tray-shaped case51 in the vicinity of one end of the first sidewall 91, and the otherend of the linear portion 58 a extends approximately parallel to thesecond sidewall 92A up to the vicinity of the fourth sidewall 93A. Theother end of the linear portion 58 a is then connected to one end of thesemi-circular curved portion 58 b, and the other end of thesemi-circular curved portion 58 b is connected to one end of the linearportion 58 c, which extends approximately parallel to the linear portion58 a to the side of the first sidewall 91. The other end of the linearportion 58 c is connected to one end of the semi-circular curved portion58 d, and the other end of the semi-circular curved portion 58 d isconnected to one end of the linear portion 58 e, which extendsapproximately parallel to the linear portion 58 c to the opposite sideof the first sidewall 91. The other end of the linear portion 58 e isconnected to one end of the semi-circular curved portion 58 f, and theother end of the linear portion 58 f is connected to one end of thelinear portion 58 g, which extends approximately parallel to the thirdsidewall 92B. The other end (on the side of the non-heating portion) ofthe linear portion 58 g is inserted through the first sidewall 91 in thevicinity of the other end of the first sidewall 91. The heater 58 has aplanar shape that is roughly symmetrical with respect to the center lineL of the steam flow entering from the steam supply ports 95A, 95B, 95C.

1. A steam cooker, comprising: a steam generator for generating steam; asteam temperature-raising device for raising a temperature of steamcoming from the steam generator; a heating chamber provided with aceiling steam outlet on its ceiling side, in which an object to becooked is heated by steam supplied from the steam temperature-raisingdevice via the ceiling steam outlet, said steam temperature-raisingdevice including: a tray-shaped case having a recessed part which has asidewall provided with a steam supply port through which steam from thesteam generator enters the recessed part, the recessed part having aplanar shape that is roughly symmetrical with respect to a center lineof a steam flow entering through the steam supply port, the tray-shapedcase being placed horizontally, with an opening of the recessed partdirected downward, on the heating chamber at the ceiling steam outlet; aheater placed in the recessed part such that a planar shape of theheater is roughly symmetrical with respect to said center line; and aspiral heat radiation fin wound around the heater and having a fin pitchof 10 mm or less.
 2. The steam cooker according to claim 1, wherein aplurality of steam outlets for supplying steam into the heating chambersideways are provided, in roughly symmetrical arrangement with respectto said center line, in sidewalls facing each other across said centerline of the recessed part of the tray-shaped case and on the oppositeside of the steam supply port.
 3. The steam cooker according to claim 1,wherein a sidewall on the opposite side of the steam supply port of therecessed part of the tray-shaped case is inclined with respect to aplane roughly perpendicular to said center line.
 4. The steam cookeraccording to claim 1, wherein the planar shape of the recessed part ofthe tray-shaped case is a generally pentagonal shape having three sidesforming a U-shape and two sides continuous with both ends of the U-shapeof the three sides and forming a generally V-shape bent outward, and thesteam supply port is provided in a sidewall corresponding to a centralone of the three sides forming the U-shape of the recessed part of thetray-shaped case.
 5. The steam cooker according to claim 1, wherein theplanar shape of the recessed part of the tray-shaped case is a shapehaving three sides forming a U-shape and an arc-shaped outer peripherythat is continuous with both ends of the U-shape of the three sides andcurves outward, and the steam supply port is provided in a sidewallcorresponding to a central one of the three sides forming the U-shape ofthe recessed part of the tray-shaped case.
 6. The steam cooker accordingto claim 4, wherein each of corners of the recessed part of thetray-shaped case has a curved surface so that adjacent sidewalls aresmoothly continuous with each other.